This invention relates to tree felling heads, particularly those of the type using circular saw blades for tree felling, and in particular to a head having a saw blade with replaceable teeth.
Tree felling disc saws such as first described in U.S. Pat. No. 4,445,552 (Hyde) and U.S. Pat. No. 4,491,163 (Kurelek) and later modified by, amongst others, U.S. Pat. No. 5,377,731 (Wildey) and U.S. Pat. No. 5,085,112 (MacLennan), are constructed to be unusually sturdy (e.g. 1 inch thick) and to cut an unusually wide kerf (e.g. 2-inches thick). The sturdiness is necessary to allow relatively poorly controlled machine travel or knuckle boom reach to be used to feed the saw through the tree. This requires a thick blade to resist bending from errant feed motion, and accordingly a wide kerf to give clearance for the blade in the cut. In addition, after the tree is cut, the designs are necessarily such that the butt of the still vertical tree does not rest on any top surface of the rotating saw, but on a fixed butt plate which is recessed into the saw, as illustrated for example in FIG. 5 (prior art). The saw's kerf must be wide enough to allow entrance of the combined thickness of this butt plate and the rotating blade and still have some clearance left over on the bottom for head drop, which occurs as a cut is completed and the weight of the tree is added to what the machinery is supporting.
It is because of these greater strength and wider kerf needs on tree felling applications that thin, commercially available circular crosscut saw blades such as those marketed by Simonds, with for example a 1/4 inch blade and 7/16 inch kerf, could not be applied to tree felling. Some early tree felling machines temporarily solved the disc strength and wide kerf needs by crudely fabricating saws with integral teeth, similar to some inexpensive cross cut saws, but from approximately one-inch thick steel plate and with alternate teeth bent up and down to cut a two-inch kerf (see for example U.S. Pat. No. 4,270,586 (Hyde et al.)).
It was thought that toughness on the job to protect against breakage from encounters with rocks was a most essential feature and that if the cutting points dulled they could be touched up with a grinder or even rebuilt by welding many times during the life of the relatively expensive steel disc. However, it soon became obvious that loggers tended not to take the time to rebuild and sharpen teeth and were running with such dull saws that power consumption was high, productivity was low and blade stresses so high that cracking at the gullets was occurring.
As it became apparent that loggers would pay more for a saw with replaceable, keener cutting teeth, various "bolt-on" ideas were devised and used. Some examples can be seen in U.S. Pat. No. 4,750,396 (Gaddis), U.S. Pat. No. 4,563,929 (Ringlee), U.S. Pat. No. 5,085,112 (MacLennan), U.S. Pat. No. 5,303,752 (MacLennan), U.S. Pat. No. 4,879,936 (Anderson), U.S. Pat. No. 5,211,212 (Carlson et al.), Des. 320,542 (Gilbert), U.S. Pat. No. 5,377,731 (Wildey) and U.S. Pat. No. 4,932,447 (Morin).
Although these devices sever trees from the stump well and some are relatively easy to maintain, they all have various drawbacks, including some which are safety-related. They all depend on threaded fasteners to retain their teeth and or tooth holders. Some have many parts (as many as 6 per tooth) which can potentially be thrown if those threaded fasteners wear out, unscrew or break.
Others with fewer parts, such as in U.S. Pat. No. 5,377,731 (Wildey) and U.S. Pat. No. 4,932,447 (Morin), have large gaps between teeth where the ends of sticks of wood can enter and be thrown. Manufacturing clearance requirements dictate the apparently excessive gap of these saws. U.S. Pat. No. 4,446,897 (Kurelek) showed a taper-held replaceable tooth in a continuous rim, but an optimal method of holding such teeth in place against cutting forces was never devised. U.S. Pat. No. 5,261,306 (Morey et al.), is exceptional in providing reduced throw probability by having a saw blade periphery advantageously contoured with bumps to at least effectively reduce the throw gap between teeth at the circumference, but tooth retention is very dependent on a threaded fastener.
The bolt and screw parts used on many tooth holding applications present many chances for error that can result in parts being dangerously thrown. For example, incorrect installation torque can result in loosening, or unseen fracture; the fasteners are vulnerable to poor quality choice or supply during servicing by the user; the screw head sockets can fill with tree gum and be difficult to remove, and hence delay timely maintenance; and the fasteners, holders and rim can be significantly weakened by wear (from wood chips and sand), which is not automatically corrected when teeth are replaced.
FIGS. 15 and 16 (prior art) illustrate the throw gap which results from several typical prior art shank and bolt tooth attachment methods. FIG. 15 shows the blade from above, and FIG. 16 shows the blade edge-on. It is known that a tangentially oriented wooden stick, somehow accidentally and rapidly fed at the saw rim of teeth, can be dangerously thrown if a radial face of a moving saw tooth can contact sufficient of the stick end grain area to instantly accelerate it to tooth tip velocity without cutting or fracturing out a relatively harmless chip of wood. The exact values of such numbers as saw rpm, tooth velocity, stick size, stick density and weight and the engagement area at which throwing rather than cutting occurs are virtually impossible to calculate and design against. However, it is reasonable to predict that for any given saw speed, the greater the gap between the face of a tooth and the back of the previous passing tooth, the more likely it is that a stick end will occasionally enter the gap sufficiently to be thrown. A stick might enter a gap from either the top or the bottom or the circumference of a saw toothed rim. It is also evident that near horizontal or tangential stick angles would most likely result in a spear-like throw if the saw does not break a chip out of the stick. A continuous smooth rim which would not be able to throw cannot be used because at least enough gap needs to be provided as a gullet to accept the wood chips being cut loose and to carry them out of the cut for expulsion.
There has thus been a need for a felling saw blade that would have a relatively smooth circumference with only enough tooth protrusion to do its share of cutting and enough gullet gap to carry its wood chips out of the kerf in the tree. In such a blade, the tooth retention method should not depend on threaded fasteners, and wear in excess of normal such as might occur on poorly maintained machines should not result in tooth parts or tooth holders being thrown, but rather the saw should cease to cut at a sufficiently productive rate, so that new teeth will have to be installed.
For the work of cross-cutting already-felled trees into logs, the saw mill industry has long known the art of using arcuate (C-shaped) replaceable teeth in circular sockets. In U.S. Pat. No. 67,682 (Strange), U.S. Pat. No. 80,929 (Disston), U.S. Pat. No. 81,811 (Miller), U.S. Pat. No. 108,059 (Smith), U.S. Pat. No. 142,258 (Miller), and U.S. Pat. No. 488,336 (Kendall), we see very early examples of single piece arcuate shaped teeth that are rotated into their sockets and held there by developing some press fit. In U.S. Pat. No. 289,715 (Risdon), U.S. Pat. No. 313,427 (Johnson), and U.S. Pat. No. 368,999 (Emerson), we see examples where an additional non-threaded fastener is used to retain the one-piece tooth against rotation in the removal direction, but not to stop rotation caused by the impact of cutting (which always rotates the tooth further into its socket). This very old art showed that rotation of the tooth in its socket from cutting forces could be stopped by providing stops in the socket to contact the tooth either at its tail or at the back of its head or both. More recent related U.S. Pat. No. 4,955,273 and U.S. Pat. No. 5,092,212 (both Pawlosky) are to the same effect.
It was thought by logging saw designers that this existing saw technology for freely cross-cutting already felled trees and logs would not stand up to the abusive job of cutting trees and brush in the woods. The saw blade with its axis vertical would have to be strong enough to, at certain times of use, support a tree bearing down on it near its circumference. At other times the weight of the felling head and part of the supporting boom would push the blade down on a stump. A much thicker blade would therefore be needed. The thickness would depend on the saw head design and the working conditions, but generally whereas cross-cut teeth are a maximum of 0.18 inches thick, various tree felling, stump clearing and brush cutting work would require tooth thicknesses mainly in the range of 1" to 21/2 thick, although other thicknesses are possible.
Merely scaling up the prior art crosscut blades and their teeth, however, is not usable in practice. There are some problems associated with attempting to do so, which the present invention overcomes.
One such problem is that the arcuate teeth of prior art cross-cut saws are designed to be installed at the required snap-in or holding press fit by a single person with a reasonable manual effort. Obviously, it would be equally desirable for the teeth of felling type saws to be installable by a single person with only reasonable manual effort. However, if with no other modifications the width of prior art teeth was increased to cut the kerf width that would be needed for tree felling, the insertion torque required would increase exponentially to unmanageable values.
Another problem is that all of the above prior art arcuate tooth inventions show that the teeth are held in their sockets against axial or twisting-out movement by a relatively steep-angled V-groove at their circumference, which engages over a V-pointed ridge which takes up the entire bore of the socket. With some modifications to arc shaping and a switch to a two piece tooth design, arcuate teeth in circular sockets are to this day held against axial movement by such steep angle V grooves. Tooth rotation torque is dependent on the forces normal to the V surfaces.
If a felling saw tooth was to be 1.8 inches thick instead of 0.18 as in a typical cross-cut saw, a simple calculation warns that the radial force to collapse the C-shape of the tooth into its socket would be ten times as great as for the cross-cut saw tooth, and that if the same V-angle was maintained, the normal forces and hence rotational torque would also be so increased, making manual tooth replacement virtually impossible.